1. Field of the Invention
The present invention relates generally to a Broadband Wireless Access (BWA) communication system, and in particular, to an apparatus and a method for fast processing downlink traffic that has been generated during a location update procedure in an idle-mode Mobile Station (MS).
2. Description of the Related Art
Provisioning of services with diverse Quality of Service (QoS) requirements at or above 100 Mbps to users is an active study area for a future-generation communication system called a 4th Generation (4G) communication system. Particularly, active research is conducted on provisioning of high-speed service by ensuring mobility and QoS to a BWA communication system such as a Wireless Local Area Network (WLAN) and a Wireless Metropolitan Area Network (WMAN). Examples of such systems are Institute of Electrical and Electronics Engineers (IEEE) 802.16a and IEEE 802.16e systems.
According to the IEEE 802.16e standards, an idle-mode MS shall update its location, if any of a plurality of location update conditions is met. The IEEE 802.16e-2005 standard defines four location update conditions: Zone Update according to change of paging group, Timer Update, Power Down Update, and Medium Access Control (MAC) Hash Skip Threshold Update.
Before describing the location update conditions, it is to be clarified that Downlink Channel Descriptor (DCD), Uplink Channel Descriptor (UCD), Mobile Paging Advertisement (MOB_PAG-ADV), Paging Group Identifier (PG-ID), MAC Hash Skip Threshold, MAC Hash Skip Counter, Deregistration Command (DREG-CMD), Ranging Request (RNG-REQ), and Ranging Response (RNG-RSP) messages are in compliance with the IEEE 802.16e-2005 standard.
In Zone Update according to change of paging group, the MS performs a location update process when it detects a change in its paging group by comparing a PG-ID stored in the MS with a PG-ID included in a DCD or MOB_PAG-ADV message broadcasted by a preferred BS during a Paging Listening Interval (PLI) known to the MS. If the two PG-IDs are different, the MS determines that its paging group has been changed.
In Timer Update, the MS periodically performs the location update process prior to the expiration of an idle-mode timer. The idle-mode timer is set to 128 to 65536 seconds as defined in IEEE 802.16e-2005 Parameters and Constants.
In Power Down Update, the MS attempts a location update as part of its orderly power-down procedure. As the MS informs its power-down to a paging controller being a network entity that handles the idle mode of the MS, the paging controller deletes information about the MS.
In MAC Hash Skip Threshold Update, the MS performs the location update process if an MS MAC Hash Skip Counter exceeds a MAC Hash Skip Threshold. The MAC Hash Skip Threshold is known from a DREG-CMD message that the MS receives from a network in order to enter the idle mode. When the location update is successful, the MS and the BS need to initialize their MAC Hash Skip Counters.
A description will be made of FIG. 1, which is a flowchart illustrating a conventional location update process when a preferred BS is changed within the same paging group.
Referring to FIG. 1, a first BS 110 and a second BS 120 are in the same paging group. When the first BS 110 is a preferred BS, an MS 100 monitors occurrence of a location update event in idle mode in step 130. Upon occurrence of a location update event, the MS 100 updates its location with the first BS 110 in step 132 and proceeds to step 134. If a location update event does not occur in step 130, the MS 100 jumps to step 134. The MS receives a MOB_PAG-ADV message from the first BS 110 during a PLI in step 134. Steps 136 to 140 are the same as steps 130 to 134 except that the preferred BS has changed to the second BS 120.
As illustrated in FIG. 1, in the case where the preferred BS changes from the first BS 110 to the second BS 120, an analysis of the occurrence of a location update event in step 136 reveals that the two BSs 110 and 120 are in the same paging group. Hence the MS jumps from step 136 to step 140 without a location update.
FIG. 2 is a diagram illustrating a signal flow for a conventional Zone Update process.
Referring to FIG. 2, when detecting a change in its paging group, the MS 200 transmits an initial ranging/dedicated ranging Code Division Multiple Access (CDMA) Code (M20) to a preferred BS, herein the BS 220, according to valid DCD and UCD information received from the BS 220.
The BS 220 transmits Uplink BandWidth (UL BW) allocation information to the MS 200 by a RNG-RSP message with status=success (M21) and a CDMA-Allocation-IE message (M22) so that the MS 200 can transmit an uplink message.
The MS 200 transmits a RNG-REQ message with ranging purpose=0x02 (M23) according to the UL BW allocation information. That is, the MS 200 sets Value of a Ranging Purpose Indication Type, Length, Value (TLV) to indicate a location update request in the RNG-REQ message with ranging purpose=0x02 (M23).
The BS 220 replies with an RNG-RSP message with location update response (M24), i.e. including a Location Update Response (LUR) TLV indicating success. The BS 220 may include paging information such as a new paging cycle, a new paging offset, and a new PG-ID in the RNG-RSP message with location update response (M24).
Upon receipt of the RNG-RSP message with location update response (M24), the MS 200 determines whether the location update is successful in step 202. If the location update is successful, the MS 200 completes the location update process in step 204. If the location update has failed, the MS 200 performs network entry initialization in step 206.
FIG. 3 is a diagram illustrating a signal flow for a conventional process for processing pending downlink traffic transmission during the Zone Update. Steps (302˜306) or messages (M20˜M24) described with reference to FIGS. 1 and 2 will not be described herein.
Referring to FIG. 3, when detecting the change of the preferred BS from a first BS 310 to a second BS 320 in a different paging group in an idle mode, i.e., when a location update event occurs, the MS 300 and the second BS 320 exchange M20 to M24 messages as illustrated in FIG. 2. Upon receipt of a RNG-RSP message with location update response (M24), the MS 300 completes the location update in step 336.
Upon receipt of the RNG-RSP message with location update response (M24), the MS 300 also monitors a valid PLI from the second BS 320 using new paging information included in the RNG-RSP message with location update response (M24). Hence, the MS 300 can receive a MOB_PAG-ADV message (M30) indicating occurrence of downlink traffic in the valid PLI.
When detecting the presence of the downlink traffic, the MS 300 releases itself from the idle mode and performs network reentry in step 338.
A network cannot be aware of a paging group of the MS 300 until the MS 300 completes the location update. In this case, if there is downlink traffic for the MS 300, a downlink traffic transmission delay may occur due to the incapability of transmitting the downlink traffic to the MS 300. The MS 300 cannot determine the occurrence of the downlink traffic until receiving the MOB_PAG-ADV message (M30), despite the completion of the location update by the time of receiving the RNG-RSP message with location update response (M24).
A shortcoming with the above conventional location update process is that the MS does not know whether downlink traffic exists for the MS even after a successful location update. The MS knows the occurrence of the downlink traffic only when an updated PLI comes.